Toxicological evaluation of a wide variety of compounds and conditions in our environment has increased in recent times. There is a growing concern over the presence of carcinogens and mutagens in the environment in which we live and work. In the work-place, concerns have been voiced about the quality of the total environment in industrial plants and offices. In connection with the studies of such environments, experimental animals have been employed and inhalation exposure apparatus have been developed with the objective of exposing such animals to environmental contaminants in order to assess their impact on the animals. On the patent side of this developing technology, reference may be made to U.S. Pat. Nos. 3,220,383; 3,557,756; 3,630,174; 3,662,713; 3,749,061; 3,765,374; 3,919,978; 3,924,571; 4,036,177; 4,085,705; 4,201,153; 4,216,741; 4,249,482; 4,343,261; 4,348,985; 4,365,590; 4,402,280 and 4,520,808. These patents are simply offered as background information and it is not intended by their listing herein that they are considered to be relevant background to this invention, but they are offered so that an independent determination may be made.
A primary problem in the design of suitable inhalation exposure apparatus is that the aerosol of the environment is not the same as that at the breathing zone of the test animal. Thus, the biological effects observed in the test animals are often not directly relatable to the actual concentrations or quality of the aerosol in the actual environment under examination. More specifically, with currently available apparatus it is very difficult to monitor and test for workplace pollution because the aerosol under examination cannot accurately be sampled and tested in an inhalation apparatus in a form which is the same as the actual environment. Aerosols tend to change upon being extracted from the environment and introduced into the inhalation chamber. Such changes are caused by a number of different factors. In order to appreciate these factors, one must understand aerosols and their properties. Aerosols are suspensions of particles in a gaseous medium. The medium acts to restrain random particle motion, supports the particles against the pull of gravity, and in some cases acts as a buffer between the particles. Aerosol particles can span the range of from near-molecular sizes up to hundreds of microns and the study of such particles involves statistical mechanics, kinetic theory and fluid dynamics. From a practical standpoint, the aerosol particles under test tend to coagulate as they are transported through various mechanical structures such as tubing, chambers and other parts of inhalation apparatus. Coagulation, also known as aggregation or agglomeration, changes the aerosol under test with the result that the aerosol in the breathing zone of the test animal does not correspond to the aerosol of the environment being tested. Other external factors have an impact upon aerosol testing such as electrical charge, condensation, turbulence, and temperature. Such external factors have inhibited the satisfactory design of inhalation exposure systems. Other complicating factors enter into the picture. For instance, methods and apparatus for handling aerosols tend to modify the chemical or physical nature of the particles suspended in the gas by such processes as evaporation and chemical reaction. Thus, experimental animals, housed in inhalation apparatus, are subjected to aerosols which are quite different from those sought to be measured in the environment outside the apparatus.
In view of the above brief background, it can be appreciated that the sampling and transportation of an aerosol from an environment under test into an inhalation chamber for exposure to an experimental animal presents special problems to the ordinary designer. There is a demand for improvements and greater reliability in aerosol testing chambers and methods.